How are Clouds Born?

What type of air is the least dense?  Warm air is less dense than cold air.  Moist air is less dense than dry air.  The least dense air of all would be air that is __________ and __________

What type of air is the least dense?  Warm air is less dense than cold air.  Moist air is less dense than dry air.  The least dense air of all would be air that is warm and moist.

How does density affect air movement?  Cold, dry air is more dense and will ____.  Warm, moist air is less dense and will ____

How does density affect air movement?  Cold, dry air is more dense and will sink.  Warm, moist air is less dense and will rise.

What about temperature?  As we rise up through the troposphere temperature will _______.  Therefore a column of warm moist air rising will get colder as it gains altitude.  This column of air will also expand due to the fact that air molecules at higher altitudes are more spread apart (less influence by gravity).  Depending on the Relative Humidity of the air it could eventually cool until it reaches _________ Temperature.

What about temperature?  As we rise up through the troposphere temperature will decrease.  Therefore a column of warm moist air rising will get colder as it gains altitude.  This column of air will also expand due to the fact that air molecules at higher altitudes are more spread apart (less influence by gravity).  Depending on the Relative Humidity of the air it could eventually cool until it reaches dewpoint Temperature.

Do the Dew!!  At dewpoint the air is ________ and can no longer hold more water vapor.  If ________ ________ are present, tiny water droplets will condense on them to form a cloud.  Once the water droplets grow in size and mass, they can drop to the earth as precipitation.

Do the Dew!!  At dewpoint the air is saturated and can no longer hold more water vapor.  If condensation nuclei are present, tiny water droplets will condense on them to form a cloud.  Once the water droplets grow in size and mass, they can drop to the earth as precipitation.

And that’s how clouds are born!

Do Now  What is the Dew Point Temperature if the air temperature is 8 ˚ and the Relative Humidity is 51%?  Answer: -2 ˚

Do Now  What is the Relative Humidity if The dry bulb is 16 ˚ and the dew point is 4 ˚?  Answer: 45%

Do Now  What is the Relative humidity of the following air mass? Dry Bulb=26˚; Dew Point=11 ˚?  Answer: 39%

Do Now  What is the Relative humidity of the following air mass? Dry Bulb=26˚; Dew Point=18 ˚?  Answer: 64%

Do Now  What is the Relative humidity of the following air mass? Dry Bulb=26˚; Dew Point=25 ˚?  Answer: 92%

Do Now  What happens to relative humidity as the difference between air temperature and dew point temperature gets smaller?  Answer: Relative Humidity increases.

Do Now  What happens to the difference between air temperature and dew point temperature as air descends? (Use the cloud base altitude chart)  Answer: It increases.

Do Now  Is a descending air mass becoming more or less humid?  Answer: Less Humid.

Orographic Effect

 A mountain can force air to rise.  As the air rises it cools and expands.  When the air reaches dew point temperature clouds form ( if condensation nuclei are present).  As the air moves past the mountain it will sink and become dry due to an increase in temperature.

Orographic Effect  The moist side of the mountain is called the windward side, and will have a lot of precipitation throughout the year.  The dry side of the mountain is called the leeward side and will often be the site of deserts.